power: qpnp-fg-gen3: add capacity learning feature

Batteries age across the time. Capacity learning is a feature
which uses the hardware autonomous coulomb counter to determine
the actual battery capacity against the advertised full capacity.
This will be useful to determine how much degradation has
happened to the battery. Capacity learning algorithm will start
based on some pre-set conditions like start SOC, battery
temperature and ends when the charging cycle is complete.

Actual capacity will be exposed through charge_full property.

Change-Id: I89cc14d213b0de10bc8d052dd76e1468fe9c30e5
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>